The particles on the wafer backside have become one of the major defect sources for many generations of technologies. Due to the technology node advancement, pitch shrinking, and an increasing number of processing steps required, the reduction of the particles on the wafer backside becomes one of the keys for the yield performance.
The electrostatic chuck (ESC) is a device for supporting the wafer. Generally, the ESC includes a plurality of support portions for supporting the wafer and a bottom area. When the ESC is manufactured, the surface of the bottom area is rough due to the material thereof. Such roughness is unable to be removed by the wet clean. When performing the dry etching process, such roughness is easy to be wiped out by the plasma to become the particles contaminating the wafer backside. Besides, the polymers generated during the semiconductor processes may fall on the bottom area of the ESC and be stuck in the rough surface thereof. Accordingly, the generated polymers are hard to remove, and also become the particles contaminating the wafer backside.
After the wafer is processed on the ESC, it will be returned to the front opening unified pod (FOUP) for temporary storage and transmission. Generally, the FOUP stores a plurality of wafers, wherein a wafer's backside faces another wafer's front side. Therefore, when a wafer is returned to the FOUP, if the backside of the wafer is contaminated by particles, the particles will fall on the front side of another wafer thereunder, thereby contaminating another wafer. Besides the problem of the particles on the wafer backside, the lifetime of the ESC will also be shortened due to the particle contamination. Hence, there is a need to solve the above problems.